With the recent remarkable innovation of the electronics, the industries of printed wiring boards are strictly urged to provide inexpensive high-density wiring boards. However, etching in the conventional subtractive method (tinting method) permits isotropic forming of a circuit pattern. With this etching technique, it is difficult to make etching in any intended direction, and provide inexpensive high-density wiring boards.
First, forming a circuit pattern by the conventional subtractive method will be described with reference to FIGS. 1(A) to 1(E):
(1) An etching resist 14 having a predetermined pattern is formed on a copper foil 12 bonded to a resin substrate 10 (as in FIG. 1(A)).
(2) Part, not covered with the etching resist 14, of the copper foil 12 is solved and removed with an etching solution that will solve the copper foil 12 to form a circuit pattern 16 (as in FIGS. 1(B) to 1(D)).
(3) The etching resist 14 remaining on the circuit pattern 16 is removed to complete the circuit pattern 16 (as in FIG. 1(E)).
As will be seen, the above anisotropic etching results in the circuit pattern 16 formed from the copper (Cu) foil 12 whose part covered with the etching resist 14 is excessively etched horizontally. This horizontal excessive etching is called “side etching”. Since a wiring interval should be determined taking the side etching in consideration in designing a high-density wiring, it is difficult to attain a high density of wiring. Therefore, an additive method by which a circuit pattern can expectantly be formed in a desired direction to a high density of wiring has been attracting attention in the field of art. However, the conventional additive method includes complicated processes and thus cannot have yielded any inexpensive printed wiring boards as final products. In this situation, it has been awaited to propose a novel processing technology using the subtractive method to provide inexpensive printed wiring boards.
For example, the Japanese Patent Application Laid Open No. 57453 of 1994 discloses a copper or copper-alloy etching component containing cupric chloride (or copper alloy), hydrochloric acid, 2-aminobenzothiazole compound and polyethylene glycol and an etching composition containing, in addition to the above etching composition, polyamine compound and its hydrochloride, sulfate and phosphate.
Also, the Japanese Patent Application Laid Open No. 2003-306784 discloses an additive that inhibits the side etching made by a ferric-chloride etching solution. This additive containing one or two or more different ones selected from among a heterocyclic compound having a carbonyl group or carboxyl group, a group of glycols each having a triple bond or a compound in which ethylene oxide is added to active hydrogen of the glycol, an alkyl sarcosine or its alkali metal salt, and anhydrate of aromatic carboxylic acid, and also at least one of thiazoles or triazoles. Also, in the Japanese Patent Application Laid Open No. 2003-306784, it is stated that the side etching-inhibiting additive may contain, as a dispersant, a well-known nonionic surface active agent, anionic surface active agent, alkyl glycol, glycol ether or the like.
However, although the Japanese Patent Application Laid Open Nos. 2003-306784 and 2003-306784 discloses the additive that will inhibit the side etching made by the cupric chloride and ferric chloride in the etching process, a most effective one selected from among such additives attains such an inhibition about 30% higher than with the conventional etching solutions and this effect of side-etching inhibition is not sufficient for forming a high-density wiring.